To better understand Earth's present tectonic style-plate tectonics—and how it may have evolved from single plate(stagnant lid) tectonics, it is instructive to consider how common it is among similar bodies in th...To better understand Earth's present tectonic style-plate tectonics—and how it may have evolved from single plate(stagnant lid) tectonics, it is instructive to consider how common it is among similar bodies in the Solar System. Plate tectonics is a style of convection for an active planetoid where lid fragment(plate) motions reflect sinking of dense lithosphere in subduction zones, causing upwelling of asthenosphere at divergent plate boundaries and accompanied by focused upwellings, or mantle plumes;any other tectonic style is usefully called "stagnant lid" or "fragmented lid". In 2015 humanity completed a 50+ year effort to survey the 30 largest planets, asteroids, satellites, and inner Kuiper Belt objects,which we informally call "planetoids" and use especially images of these bodies to infer their tectonic activity. The four largest planetoids are enveloped in gas and ice(Jupiter, Saturn, Uranus, and Neptune)and are not considered. The other 26 planetoids range in mass over 5 orders of magnitude and in diameter over 2 orders of magnitude, from massive Earth down to tiny Proteus; these bodies also range widely in density, from 1000 to 5500 kg/m^3. A gap separates 8 silicate planetoids with ρ = 3000 kg/m^3 or greater from 20 icy planetoids(including the gaseous and icy giant planets) with ρ = 2200 kg/m^3 or less. We define the "Tectonic Activity Index"(TAI), scoring each body from 0 to 3 based on evidence for recent volcanism, deformation, and resurfacing(inferred from impact crater density). Nine planetoids with TAI = 2 or greater are interpreted to be tectonically and convectively active whereas 17 with TAI <2 are inferred to be tectonically dead. We further infer that active planetoids have lithospheres or icy shells overlying asthenosphere or water/weak ice. TAI of silicate(rocky) planetoids positively correlates with their inferred Rayleigh number. We conclude that some type of stagnant lid tectonics is the dominant mode of heat loss and that plate tectonics is unusual. To make progress understanding Earth's tectonic history and the tectonic style of active exoplanets, we need to better understand the range and controls of active stagnant lid tectonics.展开更多
The history of the Hawaiian hotspot is of enduring interest in studies of plate motion and mantle flow,and has been investigated by many researchers using the detailed history of the Hawaiian-Emperor Seamount chain.On...The history of the Hawaiian hotspot is of enduring interest in studies of plate motion and mantle flow,and has been investigated by many researchers using the detailed history of the Hawaiian-Emperor Seamount chain.One of the unexplained aspects of this history is the apparent offset of several Emperor seamounts from the Hawaii plume track.Here we show that the volcanic migration rates of the Emperor seamounts based on existing data are inconsistent with the drifting rate of the Pacific plate,and indicate northward and then southward “absolute movements”of the seamounts.Numerical modeling suggests that attraction and capture of the upper part of the plume by a moving spreading ridge led to variation in the location of the plume’s magmatic output at the surface.Flow of the plume material towards the ridge led to apparent southward movement of Meiji.Then,the upper part of the plume was carried northward until 65 Ma ago.After the ridge and the plume became sufficiently separated,magmatic output moved back to be centered over the plume stem.These changes are apparent in variations in the volume of seamounts along the plume track.Chemical and isotopic compositions of basalt from the Emperor Seamount chain changed from depleted(strong mid-ocean ridge affinity)in Meiji and Detroit to enriched(ocean island type),supporting declining influence from the ridge.Although its surface expression was modified by mantle flow and by plume-ridge interactions,the stem of the Hawaiian plume may have been essentially stationary during the Emperor period.展开更多
基金supported by SNSF grant IZKOZ-2_154380partly supported by SNF 200021_149252
文摘To better understand Earth's present tectonic style-plate tectonics—and how it may have evolved from single plate(stagnant lid) tectonics, it is instructive to consider how common it is among similar bodies in the Solar System. Plate tectonics is a style of convection for an active planetoid where lid fragment(plate) motions reflect sinking of dense lithosphere in subduction zones, causing upwelling of asthenosphere at divergent plate boundaries and accompanied by focused upwellings, or mantle plumes;any other tectonic style is usefully called "stagnant lid" or "fragmented lid". In 2015 humanity completed a 50+ year effort to survey the 30 largest planets, asteroids, satellites, and inner Kuiper Belt objects,which we informally call "planetoids" and use especially images of these bodies to infer their tectonic activity. The four largest planetoids are enveloped in gas and ice(Jupiter, Saturn, Uranus, and Neptune)and are not considered. The other 26 planetoids range in mass over 5 orders of magnitude and in diameter over 2 orders of magnitude, from massive Earth down to tiny Proteus; these bodies also range widely in density, from 1000 to 5500 kg/m^3. A gap separates 8 silicate planetoids with ρ = 3000 kg/m^3 or greater from 20 icy planetoids(including the gaseous and icy giant planets) with ρ = 2200 kg/m^3 or less. We define the "Tectonic Activity Index"(TAI), scoring each body from 0 to 3 based on evidence for recent volcanism, deformation, and resurfacing(inferred from impact crater density). Nine planetoids with TAI = 2 or greater are interpreted to be tectonically and convectively active whereas 17 with TAI <2 are inferred to be tectonically dead. We further infer that active planetoids have lithospheres or icy shells overlying asthenosphere or water/weak ice. TAI of silicate(rocky) planetoids positively correlates with their inferred Rayleigh number. We conclude that some type of stagnant lid tectonics is the dominant mode of heat loss and that plate tectonics is unusual. To make progress understanding Earth's tectonic history and the tectonic style of active exoplanets, we need to better understand the range and controls of active stagnant lid tectonics.
基金supported by the National Key Research & Development Program of China (2016YFC0600408)the Strategic Priority Research Program (B) of the Chinese Academy of Sciences (XDB18020000)the Programme National de Planétologie (PNP) of the Institut des Sciences de l’Univers (INSU) of the French National Centre for Scientific Research (CNRS),co-funded by the French Space Centre (CNES) (BFC 221950)。
文摘The history of the Hawaiian hotspot is of enduring interest in studies of plate motion and mantle flow,and has been investigated by many researchers using the detailed history of the Hawaiian-Emperor Seamount chain.One of the unexplained aspects of this history is the apparent offset of several Emperor seamounts from the Hawaii plume track.Here we show that the volcanic migration rates of the Emperor seamounts based on existing data are inconsistent with the drifting rate of the Pacific plate,and indicate northward and then southward “absolute movements”of the seamounts.Numerical modeling suggests that attraction and capture of the upper part of the plume by a moving spreading ridge led to variation in the location of the plume’s magmatic output at the surface.Flow of the plume material towards the ridge led to apparent southward movement of Meiji.Then,the upper part of the plume was carried northward until 65 Ma ago.After the ridge and the plume became sufficiently separated,magmatic output moved back to be centered over the plume stem.These changes are apparent in variations in the volume of seamounts along the plume track.Chemical and isotopic compositions of basalt from the Emperor Seamount chain changed from depleted(strong mid-ocean ridge affinity)in Meiji and Detroit to enriched(ocean island type),supporting declining influence from the ridge.Although its surface expression was modified by mantle flow and by plume-ridge interactions,the stem of the Hawaiian plume may have been essentially stationary during the Emperor period.
